Manufacturers of so-called noncarpeted auxiliary floor mats, such as those used in automobiles, generally have been limited to using thermoset compounds, such as those determined to be in the broad category of rubbers. Thermoset compounds are not considered to be 100% recyclable since the material undergoes a chemical change during the curing process. Due to this chemical change, the material cannot be simply remelted and formed back into a similar product. Mats manufactured from thermoset materials are typically produced in a compression molding process requiring relatively low compression pressures, such as on the order of 50-250 psi, but relatively long process cycle times that allow for the chemical reaction to take place during the curing process. These cycle times can be on the order of 180-300 seconds.
In conventional thermoset rubber compression molding processes, the rubber is generally prepared in the form of a slab or so-called pre-prep prior to its placement within a mold. The mold is basically comprised of two sections defining a mold cavity, but has also included more sophisticated multiple sections to form the mold cavity. To provide a surface finish suitable for the automotive industry Class A rating, for example, the manufacturer needs to accurately control the molding process to assure that the rubber material provides a flow front which pushes the air within the mold cavity away from the surfaces of the molding tool. Additionally, the manufacturer may incorporate a slow close process or bump steps in the molding cycle to remove air and other volatiles in the rubber compound from the surface of the tool. These processes assure fuller contact of the rubber compound with the mold surface but also increase the necessary process cycle time. In these processes, direct, continuous contact of the rubber with the surface of the mold is necessary to create an outer surface in the final product which is free of blemishes caused by air bubbles and/or voids. Full contact of the rubber with the mold surface also allows the product to pick up the grain or surface finish texture of the interior mold surface.
In addition to compression molding, injection molding of thermoset materials has been used to produce noncarpeted auxiliary floor mats which exhibit surface finishes considered to be Class A. However, disadvantages as found in compression molding are also experienced with injection molding techniques. These include long manufacturing cycle times and floor mats that are heavier than desired and not fully or easily recyclable. Injection molding processes may also be used to produce thermoplastic products which are easier to recycle. However, these processes require high molding pressures ranging from 2000 to 6000 psi. Injection molding processes generally have a number of material limitations and process limitations that make producing a floor mat with varying cross sectional thickness difficult.
Floor mats having a varying cross sectional thickness are considered to be difficult to injection mold as the process itself introduces many stresses into the material. This is due to the variable time required to cool the different cross sectional thicknesses. These stresses introduced by the injection molding process cause warpage which not only detracts from the appearance of the finished product but often fails to meet the physical tolerance specifications of these products.
Another process in the prior art for producing noncarpeted floor mats from thermoplastic materials is known as an extrusion/embossing process using matched metal rolls. In this process, it is possible to produce floor mats with some variable cross sectional thicknesses, however, the detail and design of the surface geometry and the finish is more limited than in similar products, such as those produced by injection molding. This process also is susceptible to warpage in the finished product due to the inability to evenly cool the variable cross sectional thicknesses. Thus, floor mats produced according to such processes cannot meet the stringent design and geometrical tolerancing often required, for example, by the automotive industry.
To address problems such as those problems mentioned above, it would be desirable to provide methods and apparatus for forming a noncarpeted thermoplastic floor mat in an efficient, cost effective, yet high quality manner.